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Glossary of biology

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This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices.


abiotic component
Any non-living chemical or physical part of the environment that affects living organisms and the functioning of ecosystems, such as the atmosphere and water resources.
The shedding of flowers, leaves, and/or fruit following formation of scar tissue in a plant.
A process in which one substance permeates another. A fluid permeates or is dissolved by a liquid or solid. Skin absorption is a route by which substances can enter the body through the skin.
absorption spectrum
The spectrum of electromagnetic radiation that has passed through a medium which absorbs radiation of certain wavelengths.
Adaptation to a new climate, as with a new temperature or altitude or environment.
A molecule that participates in many biochemical reactions in protein, carbohydrate, and lipid metabolism, notably the citric acid cycle.
A type of animal, such as a flatworm or a jellyfish, with a body plan that lacks a fluid-filled cavity between the body wall and the digestive tract. Rather, semi-solid mesodermal tissues between the gut and body wall hold the animal's organs in place. Contrast coelomate and pseudocoelomate.
action potential
The local change in voltage that occurs when the membrane potential of a specific location along the membrane of a cell rapidly depolarizes, such as when a nerve impulse is transmitted between neurons.
activation energy
The energy that an atomic system must acquire before a process (such as an emission or reaction) can occur.
active site
The part of an enzyme or antibody at which substrate molecules bind and undergo a chemical reaction.
active transport
Transport of a substance (such as a protein or drug) across a cell membrane against a concentration gradient. Unlike passive transport, active transport requires an expenditure of energy.
adaptive radiation
The process by which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new niches.
A purine-derived organic compound which is one of the four canonical nucleobases used in the nucleic acids DNA and RNA. Its derivatives are involved in a wide variety of biochemical reactions, including cellular respiration.

adenosine triphosphate (ATP)
An organic compound derived from adenine that functions as the major source of energy for chemical reactions inside living cells. It is found in all forms of life and is often referred to as the "molecular currency" of intracellular energy transfer.
adipose tissue
A type of loose connective tissue made of mostly adipocytes and found in human and animal tissue, where it is colloquially known as body fat.
Capable of surviving and growing in the presence of oxygen.
The study of organic particles which are passively transported by the air, including bacteria, fungal spores, very small insects, pollen grains, and viruses.
The practice of cultivating land, growing food, and/or raising livestock.
The study of plant nutrition and growth, especially as a way to increase crop yield.

(pl.) algae

Any member of a diverse polyphyletic group of photosynthetic, eukaryotic, mostly aquatic organisms ranging from simple unicellular microalgae to massive colonial or multicellular forms such as kelp. Algae may reproduce sexually or asexually, and are often compared to plants, though they lack most of the complex cell and tissue types that characterize true plants.
allopatric speciation
A form of speciation which occurs when biological populations of the same species become isolated from each other to an extent that prevents or interferes with genetic interchange.
amino acid
A class of organic compounds containing an amine group and a carboxylic acid group which function as the fundamental building blocks of proteins and play important roles in many other biochemical processes.
An organism which produces an egg composed of a shell and membranes that creates a protected environment in which the embryo can develop out of water.
analogous structures
A set of morphological structures in different organisms which have similar form or function but were not present in the organisms' last common ancestor. The cladistic term for the same phenomenon is homoplasy.
The branch of biology that studies the structure and morphology of living organisms and their various parts.
Any member of a clade of multicellular eukaryotic organisms belonging to the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, reproduce sexually, and grow from a blastula during embryonic development. An estimated 7 million distinct animal species currently exist.

Also called an antibacterial.

A type of antimicrobial drug used in the treatment and prevention of bacterial infections.
The scientific study of spiders, scorpions, pseudoscorpions, and harvestmen, collectively called arachnids.
artificial selection

Also called selective breeding.

The process by which humans use animal breeding and plant breeding to selectively control the development of particular phenotypic traits in organisms by choosing which individual organisms will reproduce and create offspring. While the deliberate exploitation of knowledge about genetics and reproductive biology in the hope of producing desirable characteristics is widely practiced in agriculture and experimental biology, artificial selection may also be unintentional and may produce unintended (desirable or undesirable) results.
asexual reproduction
A type of reproduction involving a single parent that results in offspring that are genetically identical to the parent.
The branch of biology concerned with the effects of outer space on living organisms and the search for extraterrestrial life.
The system of immune responses of an organism directed against its own healthy cells and tissues.

Sometimes used interchangeably with primary producer.

An organism capable of producing complex organic compounds from simple substances present in its surroundings, generally by using energy from sunlight (as in photosynthesis) or from inorganic chemical reactions (as in chemosynthesis). Autotrophs do not need to consume another living organism in order to obtain energy or organic carbon, as opposed to heterotrophs.

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B cell
A type of lymphocyte in the humoral immunity of the adaptive immune system.
An enormous and diverse clade of microscopic, prokaryotic, single-celled organisms which lack a true nucleus. They represent one of the three fundamental biological domains.
A virus that infects and multiplies within bacteria.
Barr body
The inactive X chromosome in a female somatic cell, rendered inactive in a process called lyonization, in those species in which sex is determined by the presence of the Y (including humans) or W chromosome rather than the diploidy of the X or Z.
basal body
An organelle formed from a centriole, and a short cylindrical array of microtubules. Also called a basal granule, a kinetosome, and in older cytological literature, a blepharoplast.
behavioral ecology
The study of the evolutionary basis for animal behavior due to ecological pressures.
A dark green to yellowish-brown fluid, produced by the liver of most vertebrates, which aids the digestion of lipids in the small intestine. Also called gall.
binary fission
The process by which one prokaryotic cell divides into two identical daughter cells.
binomial nomenclature
A formal system of classifying species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages.
The process of catalysis in biological systems. In biocatalytic processes, natural catalysts, such as protein enzymes, perform chemical transformations on organic compounds.
The branch of biology that studies the chemical properties, compositions, reactions, and processes related to living organisms.
A contraction of "biological diversity" generally referring to the variety and variability of life on Earth.
The application of concepts and methods of biology to solve real-world problems related to the life sciences or the application thereof.
The study of the transformation of energy in living organisms.
The study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, isolation and habitat area.
The application of computer technology to the management of biological information.
biological organization
The hierarchy of complex biological structures and systems, designed to define life through a reductionist approach.
The study of life and living organisms.
Organic matter derived from living or recently living organisms. Biomass can be used as a source of energy and it most often refers to plants or plant-based materials which are not used for food or feed, and are specifically called lignocellulosic biomass.
The theoretical use of mathematical models and abstractions of living systems to understand and predict biological problems.
Any very large ecological area on the Earth's surface containing fauna and flora (animals and plants) adapting to their environment. Biomes are often defined by abiotic factors such as climate, topographical relief, geology, soils, and water resources.
The study of the structure and function of biological systems by means of the methods of "mechanics", which is the branch of physics involving analysis of the actions of forces.
biomedical engineering
The application of engineering principles and design concepts to medicine and biology for healthcare purposes (e.g. diagnostic or therapeutic).
biomedical research
The pursuit of answers to medical questions. These investigations lead to discoveries, which in turn lead to the development of new preventions, therapies, and cures for problems in human and veterinary health. Biomedical research generally takes two forms: basic science and applied research.
Molecules and ions that are present in organisms, essential to some typically biological process such as cell division, morphogenesis, or development.
The application of approaches traditionally employed in physics to study biological systems.
Biotechnology is the use of living systems and organisms to develop or make products, or "any technological application that uses biological systems, living organisms or derivatives thereof, to make or modify products or processes for specific use" (UN Convention on Biological Diversity).
A form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs.
A mammalian blastula in which some differentiation of cells has occurred.
A body fluid that circulates in humans and other vertebrate animals and is generally responsible for delivering necessary substances such as oxygen and nutrients between the cells and tissues of the body and transporting metabolic waste products away from those same cells and tissues.
blood-brain barrier
A semipermeable membrane separating the blood from the cerebrospinal fluid, and constituting a barrier to the passage of cells, particles, and large molecules.
The branch of biology that studies plants.
building biology
A science that leads to natural healthy ecological homes, schools, and workplaces that exist in harmony with the environment.

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Calvin cycle
The Calvin cycle, light-independent reactions, bio synthetic phase, dark reactions, or photosynthetic carbon reduction (PCR) cycle[1] of photosynthesis are the chemical reactions that convert carbon dioxide and other compounds into glucose. These reactions occur in the stroma, the fluid-filled area of a chloroplast outside the thylakoid membranes. These reactions take the products (ATP and NADPH) of light-dependent reactions and perform further chemical processes on them. There are three phases to the light-independent reactions, collectively called the Calvin cycle: carbon fixation, reduction reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration.
carbon fixation
The conversion process of inorganic carbon (carbon dioxide) to organic compounds by living organisms.
Any member of two classes of chemical compounds derived from carbonic acid or carbon dioxide.
One of a class of organic pigments produced by algae and plants, as well as certain bacteria and fungi.
An enzyme found in nearly all living organisms exposed to oxygen, including bacteria, plants, and animals.
The basic structural and functional unit of all living organisms, and the smallest functional unit of life. A cell may exist as an independent, self-replicating unit (as in the case of unicellular organisms), or in cooperation with other cells, each of which may be specialized for carrying out particular functions within a larger multicellular organism. Cells consist of cytoplasm enclosed within a cell membrane and sometimes a cell wall, and serve the fundamental purpose of separating the controlled environment in which biochemical processes take place from the outside world. Most cells are visible only under a microscope.
cell biology

Also called cytology.

The branch of biology that studies the structure and function of living cells, including their physiological properties, metabolic processes, chemical composition, life cycle, the organelles they contain, and their interactions with their environment. This is done at both microscopic and molecular levels.
cell cycle
cell division
Any process by which a parent cell divides into two or more daughter cells. Examples include binary fission, mitosis, and meiosis.
cell membrane
The semipermeable membrane surrounding the cytoplasm of a cell.

cell nucleus
The "control room" for the cell. The nucleus gives out all the orders.
cell plate
Grown in the cell's center, it fuses with the parental plasma membrane, creating a new cell wall that enables cell division.
cell theory
The theory that all living things are made up of cells.
cell wall
A tough, often rigid structural barrier surrounding certain types of cells (such as in fungi, plants, and most prokaryotes) that is immediately external to the cell membrane.
Of or relating to a cell.
central dogma of molecular biology
A framework for understanding the movement of genetic information between information-carrying biopolymers within biological systems. Popularly (though simplistically) stated as "DNA makes RNA and RNA makes protein", the principle attempts to capture the notion that the transfer of genetic information only naturally occurs between certain classes of molecules and in certain directions.
A cylindrical cell structure[1] composed mainly of a protein called tubulin that is found in most eukaryotic cells.
An organelle that is the main place where cell microtubules get organized, occurring only in plant and animal cells and regulating the cell division cycle.
chemical compound
A chemical substance consisting of two or more different chemically bonded elements, with a fixed ratio determining the composition. The ratio of each element is usually expressed by a chemical formula.
chemical equilibrium
The state in which both reactants and products are present in concentrations which have no further tendency to change with time in a chemical reaction.
chemical reaction
A process that leads to the transformation of one set of chemical substances to another.
A branch of the physical sciences that studies the composition, structure, properties, and change of matter. Chemical interactions underlie all biological processes.
Any of several photosynthetic pigments found in cyanobacteria, algae, or plants.
Organelles, specialized subunits, in plant and algal cells, main role of which is to conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight and converts and stores it in the energy-storage molecules ATP and NADPH while freeing oxygen from water.
An organic molecule, a sterol, a type of lipid molecule, and biosynthesized by all animal cells because it is an essential structural component of all animal cell membranes—essential to maintain both membrane structural integrity and fluidity.
A threadlike strand of DNA in the cell nucleus that carries the genes in a linear order.
citric acid cycle

Also called the Krebs cycle and tricarboxylic acid cycle (TCA).

A series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats and proteins into carbon dioxide and chemical energy in the form of guanosine triphosphate (GTP). In addition, the cycle provides precursors of certain amino acids as well as the reducing agent NADH that is used in numerous other biochemical reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest established components of cellular metabolism and may have originated abiogenically.
clonal selection
Clonal selection theory is a scientific theory in immunology that explains the functions of cells (lymphocytes) of the immune system in response to specific antigens invading the body. The theory has become the widely accepted model for how the immune system responds to infection and how certain types of B and T lymphocytes are selected for destruction of specific antigens.[2]
The process of producing similar populations of genetically identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually.
conservation biology
The scientific study of nature and of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions.
convergent evolution
The independent development of similar characteristics in species of different lineages.
countercurrent exchange
A mechanism that happens in nature and is mimicked in industry and engineering, in which there is a crossover of some property, usually heat or some component, between two flowing bodies flowing in opposite directions to each other.
A fold in the inner membrane of a mitochondrion.
The branch of biology that studies the effects of low temperatures on living things within Earth's cryosphere or in laboratory experiments.
See cell biology.
All of the material within a cell and enclosed by the cell membrane, except for the nucleus. The cytoplasm consists mainly of water, the gel-like cytosol, various organelles, and free-floating granules of nutrients and other biomolecules.
One of the four main nucleotide bases found in DNA and RNA, along with adenine, guanine, thymine, and uracil (in RNA); it is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at position 2).
A cytoskeleton is present in the cytoplasm of all cells, including bacteria, and archaea. It is a complex, dynamic network of interlinking protein filaments that extends from the cell nucleus to the cell membrane.[3] The cytoskeletal systems of different organisms are composed of similar proteins. In eukaryotes, the cytoskeletal matrix is a dynamic structure composed of three main proteins, which are capable of rapid growth or disassembly dependent on the cell's requirements.[4]

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Darwinian fitness
The genetic contribution of an individual to the next generation's gene pool relative to the average for the population, usually measured by the number of offspring or close kin that survive to reproductive age.
Deciduous means "falling off at maturity" or "tending to fall off", and it is typically used in order to refer to trees or shrubs that lose their leaves seasonally (most commonly during autumn) and to the shedding of other plant structures such as petals after flowering or fruit when ripe.
dehydration reaction
A chemical reaction that involves the loss of a water molecule from the reacting molecule.
A process in which proteins or nucleic acids lose the quaternary, tertiary and secondary structure which is present in their native state, by application of some external stress or compound such as a strong acid or base, a concentrated inorganic salt, or an organic solvent.
A short branched extension of a nerve cell, along which impulses received from other cells at synapses are transmitted to the cell body.
A microbially facilitated process of nitrate reduction (performed by a large group of heterotrophic facultative anaerobic bacteria) that may ultimately produce molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Part of the nitrogen cycle.

deoxyribonucleic acid (DNA)
A nucleic acid polymer that serves as the fundamental hereditary material in all living organisms. A set of four bases is used in the nucleotide sequences which comprise each DNA molecule: adenine (abbreviated A), cytosine (C), guanine (G), and thymine (T); these four bases are individually attached to a sugar-phosphate complex to form a complete nucleotide.
The process of reversing the charge across a cell membrane (such as that of a neuron), thereby causing an action potential. In depolarization, the inside of the membrane, which is normally negatively charged, becomes positive and the outside becomes negative. This is brought about by positive sodium ions rapidly passing into the axon.

Also called macula adhaerens.

A cell structure specialized for cell-to-cell adhesion.
developmental biology
The branch of biology that studies the processes by which living organisms grow and develop over time. The field may also encompass the study of reproduction, regeneration, metamorphosis, and the growth and differentiation of stem cells in mature tissues.
See deoxyribonucleic acid.
DNA replication
The replication of a DNA molecule; the process of producing two identical copies from one original DNA molecule, in which the double helix is unwound and each strand acts as a template for the next strand; nucleotide bases are matched to synthesize the new partner strands.
DNA sequencing
The process of determining the precise order of nucleotides within a DNA molecule.
A motor protein (also called molecular motor or motor molecule) in cells which converts the chemical energy contained in ATP into the mechanical energy of movement.

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ecological efficiency
The efficiency with which energy is transferred from one trophic level to the next. It is determined by a combination of efficiencies relating to organismic resource acquisition and assimilation in an ecosystem. Primary production occurs in autotrophic organisms of an ecosystem.
ecological pyramid
An ecological pyramid (also trophic pyramid, eltonian pyramid, energy pyramid, or sometimes food pyramid) is a graphical representation designed to show the biomass or bio productivity at each trophic level in a given ecosystem. Biomass is the amount of living or organic matter present in an organism.
ecological succession
The more or less predictable and orderly set of changes that occurs in the composition or structure of an ecological community over time.
The scientific analysis and study of interactions between organisms and their environment. It is an interdisciplinary field that includes biology, geography, and Earth science.
A biological discipline that studies the adaptation of an organism's physiology to environmental conditions.
A community of living organisms in conjunction with the non-living components of their physical environment, interacting as a system.

Sometimes called an ecospecies.

In evolutionary ecology, a genetically distinct geographic variety, population, or race within a species which is adapted to specific environmental conditions.
The outermost layer of cells or tissue of an embryo in early development, or the parts derived from this, which include the epidermis, nerve tissue, and nephridia.
An organism in which internal physiological sources of heat are of relatively small or quite negligible importance in controlling body temperature. Colloquially, these organisms often referred to as "cold-blooded".
A small molecule that selectively binds to a protein and regulates its biological activity. In this manner, effector molecules act as ligands that can increase or decrease enzyme activity, gene expression, or cell signaling.
Conducted or conducting outwards or away from something (for nerves, the central nervous system; for blood vessels, the organ supplied). Contrast afferent.
The organic vessel containing the zygote in which an animal embryo develops until it can survive on its own, at which point the developing organism emerges from the egg in a process known as hatching.
electrochemical gradient
A gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts: the electrical potential and the difference in chemical concentration across the membrane.
electromagnetic spectrum
The range of all possible frequencies of electromagnetic radiation. When referring to an object, the electromagnetic spectrum is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object.
A negatively charged subatomic particle, symbolized by e− or β−.
electron acceptor
An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process.
electron carrier
electron carrier. Any of various molecules that are capable of accepting one or two electrons from one molecule and donating them to another in the process of electron transport. As the electrons are transferred from one electron carrier to another, their energy level decreases, and energy is released.
electron donor
An electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process.
electron microscope
The electron microscope is a type of microscope that uses a beam of electrons to create an image of the specimen. It is capable of much higher magnifications and has a greater resolving power than a light microscope, allowing it to see much smaller objects in finer detail.
electron transport chain
The site in a mitochondrion of oxidative phosphorylation in eukaryotes. The NADH and succinate generated by the citric acid cycle are oxidized, providing energy to power ATP synthase. Photosynthetic electron transport chain of the thylakoid membrane.
A developing stage of a multicellular organism.
The branch of biology that studies the development of gametes (sex cells), fertilization, and development of embryos and fetuses. Additionally, embryology involves the study of congenital disorders that occur before birth.
endangered species
Endangered species are threatened by factors such as habitat loss, hunting, disease and climate change, and usually, endangered species, have a declining population or a very limited range.
The ecological state of an organism or species being unique to a defined geographic location, such as an island, nation, country, habitat type, or other defined zone. Organisms are said to be endemic to a place if they are indigenous to it and found nowhere else.
endergonic reaction

Also called a nonspontaneous reaction or unfavorable reaction.

A type of chemical reaction in which the standard change in free energy is positive, and energy is absorbed.
endocrine gland
A gland of the animalian endocrine system that secretes hormones directly into the blood rather than through a duct. In humans, the major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus, and adrenal glands.
endocrine system
The collection of glands that produce hormones which regulate metabolism, growth and development, tissue function, and a wide variety of other biological processes.
A form of active transport in which a cell transports molecules such as proteins into the cell's interior by engulfing them in an energy-consuming process.
One of the three primary germ layers in the very early human embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer), with the endoderm being the innermost layer.
endoplasmic reticulum
A type of organelle found in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae.
The tissue produced inside the seeds of most of the flowering plants following fertilization.
endosymbiotic theory
An evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms, first articulated in 1905 and 1910 by the Russian botanist Konstantin Mereschkowski, and advanced and substantiated with microbiological evidence by Lynn Margulis in 1967.
An organism that maintains its body at a metabolically favorable temperature, largely by the use of heat set free by its internal bodily functions instead of relying almost purely on ambient heat.
Entomology is the study of insects, but etymology is the study of words.
environmental biology
the branch of biology concerned with the relations between organisms and their environment. bionomics, ecology. biological science, biology - the science that studies living organisms. palaeoecology, paleoecology - the branch of ecology that studies ancient ecology.
Enzymes are biological molecules (proteins) that act as catalysts and help complex reactions occur everywhere in life. Let's say you ate a piece of meat. Proteases would go to work and help break down the peptide bonds between the amino acids.
Epidemiology is the study and analysis of the patterns, causes, and effects of health and disease conditions in defined populations. It is the cornerstone of public health, and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare.
A sub-field of genetics that studies cellular and physiological phenotypic trait variations caused by external or environmental factors which affect how cells express genes, as opposed to those caused by changes in the DNA sequence.
An organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, marine environments or from debris accumulating around it.
essential nutrient
The primary female sex hormone.
The scientific study of non-human animal behaviour (i.e. excluding human behaviour) and usually with a focus on behaviour under natural conditions, and viewing behaviour as an evolutionarily adaptive trait.
Organisms whose cells have a nucleus enclosed within membranes, unlike Prokaryotes (Bacteria and other Archaea).
The change in the heritable characteristics of populations of biological organisms over successive generations, which may occur by mutation, gene flow, natural selection, or random chance.
evolutionary biology
Evolutionary biology is the subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth starting from a single origin of life. These processes include the descent of species, and the origin of new species.
A form of active transport and bulk transport in which a cell transports molecules out of the cell by expelling them through an energy-dependent process.
exponential growth
It is exhibited when the rate of change of the value of a mathematical function is proportional to the function's current value, resulting in its value at any time being an exponential function of time.
external fertilization
A type of fertilization in which a sperm unites with an egg external to the body or bodies of the parent organisms. Contrast internal fertilization.
Of or occurring in the space outside the plasma membrane of a cell. Contrast intracellular.
extranuclear inheritance
A transmission of genes that take place outside the nucleus.

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facultative anaerobe
An organism which is capable of producing energy through aerobic respiration and then switching to anaerobic respiration depending on the amounts of oxygen and fermentable material in the environment.
A metabolic process that consumes sugar in the absence of oxygen.
fitness landscape

Also spelled foetus.

An animal embryo after eight weeks of development.

(pl.) flagella

A lash-like appendage that protrudes from the cell body of certain bacterial and eukaryotic cells.

flavin adenine dinucleotide (FAD)
A redox cofactor, more specifically a prosthetic group of a protein, involved in different important enzymatic reactions in metabolism.
food chain
The chain of eating and getting nutrition which starts from a small herbivores animal and ends up at a big carnivorous organism.
founder effect
A loss of genetic variation that takes places when a new population is established by a very small number of individuals from a larger population.

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G protein
A family of proteins that act as molecular switches inside cells, and are implicated in transmitting signals from a diversity of stimuli outside a cell to its interior.
Any segment of DNA that contains the information necessary to produce a functional RNA and/or protein product in a controlled manner. Genes are often considered the fundamental molecular units of heredity. The transmission of genes from a parent cell or organism to its offspring is the basis of the inheritance of phenotypic traits.
gene pool
A set of all genes, or genetic information, in any population, usually of a particular species.
genetic code
A set of rules used by living cells to translate information encoded within genetic material (DNA or mRNA sequences) into proteins.
genetic drift
An alteration in the frequency of an existing gene variant in a population due to random sampling of organisms.
genetic variation
Variations of genomes between members of species, or between groups of species thriving in different parts of the world as a result of genetic mutation. Genetic diversity in a population or species is a result of new gene combinations (e.g. crossing over of chromosomes), genetic mutations, genetic drift, etc.
The study of heredity.
The entire set of genetic material contained within the chromosomes of an organism, organelle, or virus.
Part of the genetic makeup of a cell, and therefore of an organism or individual, which determines one of its characteristics (phenotype).
An organ found in the digestive tract of some animals, including archosaurs (pterosaurs, crocodiles, alligators, and dinosaurs, including birds), earthworms, some gastropods, some fish, and some crustaceans.
One of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA).

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A place for animals, people, and plants and non-living things.
A form of learning in which an organism decreases or desists its responses to a stimulus after repeated or prolonged presentations .
The passing on of phenotypic traits from parents to their offspring, either through sexual or asexual reproduction. Offspring cells and organisms are said to inherit the genetic information of their parents.
A sexually reproducing organism with both male and female reproductive organs.
The branch of zoology that studies reptiles and amphibians.
The improved or increased function of any biological quality in a hybrid offspring.
The study of the microscopic anatomy of cells and tissues of plants and animals.
Any member of a class of signaling molecules produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behaviour.
Any living organism that harbors another living organism (known as a "guest" or symbiont), whether the guest is parasitic, mutualistic, or commensalist in its interactions with the host. The guest typically receives shelter and nourishment from the host.
An organic compound consisting entirely of hydrogen and carbon atoms. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarbyls.

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The branch of biology devoted to the study of fish, including bony fishes (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha).
immune response
The immune response is how your body recognizes and defends itself against bacteria, viruses, and substances that appear foreign and harmful.
Glycoprotein molecules produced by plasma cells (white blood cells) which act as a critical part of the immune response by specifically recognizing and binding to particular antigens, such as bacteria or viruses, and aiding in their destruction. Also known as antibodies.
The invasion of an organism's cells or tissues by a disease-causing pathogen, its growth and/or multiplication, and the reaction of the host organism to the infectious agent and the toxins it produces. The variety of biological pathogens capable of causing infections includes certain bacteria, viruses, fungi, protists, parasitic worms, and arthropods.
Insulin helps keeps your blood sugar level from getting too high (hyperglycemia) or too low (hypoglycemia). ... After you eat food and your blood sugar level rises, cells in your pancreas (known as beta cells) are signaled to release insulin into your bloodstream.
integrative biology
The various forms of cross-disciplinary and multitaxon research.
A group of signaling proteins made and released by host cells in response to the presence of several pathogens, such as viruses, bacteria, parasites, and also tumor cells. In a typical scenario, a virus-infected cell will release interferons causing nearby cells to heighten their antiviral defenses.
internal fertilization
A type of fertilization which takes place inside the egg-producing individual.
International System of Units
(French: Système international d'unités; abbreviated SI) The modern form of the metric system, and the most widely used system of measurement.
Of or occurring inside or within the enclosed interior of a cell. Contrast extracellular.
introduced species
A group of animals that have no backbone, unlike animals such as reptiles, amphibians, fish, birds and mammals, which all have a backbone.
An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.
ionic bond
The complete transfer of valence electron(s) between atoms. It is a type of chemical bond that generates two oppositely charged ions. In ionic bonds, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively charged anion.
A molecule with the same chemical formula as another molecule, but with a different chemical structure. That is, isomers contain the same number of atoms of each element, but have different arrangements of their atoms.
isotonic solution
Refers to two solutions having the same osmotic pressure across a semipermeable membrane. This state allows for the free movement of water across the membrane without changing the concentration of solutes on either side.

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The midsection of the small intestine of many higher vertebrates like mammals, birds, and reptiles. It is present between the duodenum and the ileum.


An enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates.
Krebs cycle
See citric acid cycle.


(pl.) larvae
A distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development, such as insects, amphibians, or cnidarians, typically have a larval phase of their life cycle.
Law of Independent Assortment
The principle, originally formulated by Gregor Mendel, stating that when two or more characteristics are inherited, individual hereditary factors assort independently during gamete production, giving different traits an equal opportunity of occurring together.
A colourless cell which circulates in the blood and body fluids and is involved in counteracting foreign substances and disease; sometimes called a white blood cell. There are several types, all amoeboid cells with a nucleus, including lymphocytes, granulocytes, and monocytes.
life cycle
The fibrous connective tissue that connects bones to other bones and is also known as articular ligament, articular larua, fibrous ligament, or true ligament.
light-independent reactions
See Calvin cycle.
linked genes
Any set of one or more genes which are sufficiently close together on the same chromosome that they are very unlikely to assort independently and therefore are usually inherited together.
A substance that is insoluble in water and soluble in alcohol, ether, and chloroform. Lipids are an important component of living cells. Together with carbohydrates and proteins, lipids are the main constituents of plant and animal cells. Cholesterol and triglycerides are lipids.
A biochemical assembly that contains both proteins and lipids, bound to the proteins, which allow fats to move through the water inside and outside cells. The proteins serve to emulsify the lipid molecules.

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M phase
Mitosis and cytokinesis together define the mitotic (M) phase of an animal cell cycle – the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell.
Evolution on a scale of separated gene pools. Macroevolutionary studies focus on change that occurs at or above the level of species, in contrast with microevolution, which refers to smaller evolutionary changes (typically described as changes in allele frequencies) within a species or population.
A very large molecule, such as a protein, commonly created by polymerization of smaller subunits (monomers). They are typically composed of thousands or more atoms.
Nutrients needed in large amounts which provide calories or energy. Nutrients are substances needed for growth, metabolism, and for other body functions. There are three basic types of macronutrients: fats, proteins, and carbohydrates.
A kind of swallowing cell, which means it functions by literally swallowing up other particles or smaller cells. Macrophages engulf and digest debris (like dead cells) and foreign particles through the process of phagocytosis, so macrophages act like scavengers.
The study of mammals, a class of vertebrates with characteristics such as homeothermic metabolism, fur, four-chambered hearts, and complex nervous systems.
marine biology
The study of organisms in the ocean or other marine bodies of water. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather than on taxonomy.
mast cell
A cell filled with basophil granules, found in numbers in connective tissue and releasing histamine and other substances during inflammatory and allergic reactions.
The continuation of the spinal cord within the skull, forming the lowest part of the brainstem and containing control centres for the heart and lungs.
A specialized type of cell division in which a dividing parent cell proceeds through two consecutive divisions, ultimately producing four genetically unique daughter cells in each of which the chromosome number is half of that in the original parent cell. This process is exclusive to cells of the sex organs in sexually reproducing eukaryotes, where it serves the purpose of generating gametes such as eggs, sperm, or spores.
membrane potential
When a nerve or muscle cell is at "rest", its membrane potential is called the resting membrane potential. In a typical neuron, this is about –70 millivolts (mV). The minus sign indicates that the inside of the cell is negative with respect to the surrounding extracellular fluid.
messenger RNA
A large family of RNA molecules that convey genetic information from DNA to the ribosome.
The third phase of mitosis, in which duplicated genetic material carried in the nucleus of a parent cell is separated into two identical daughter cells. During metaphase, the cell's chromosomes align themselves in the middle of the cell through a type of cellular "tug of war".
The study of microscopic organisms, such as bacteria, viruses, archaea, fungi and protozoa. This discipline includes fundamental research on the biochemistry, physiology, cell biology, ecology, evolution and clinical aspects of microorganisms, including the host response to these agents.
The alteration in allele frequencies that occurs over time within a population.

(sing.) mitochondrion

In eukaryotic cells, the part of the cell cycle during which the division of the nucleus takes place and duplicated chromosomes are separated into two distinct nuclei. Mitosis is generally preceded by the "S" stage of interphase, when the cell's DNA is replicated, and followed by cytokinesis, when the cytoplasm and cell membrane are divided into two new daughter cells. It is similar to but distinct from binary fission and meiosis.
The smallest particle in a chemical element or compound that has the chemical properties of that element or compound. Molecules are made up of atoms that are held together by chemical bonds. These bonds form as a result of the sharing or exchange of electrons among atoms.
molecular biology
The branch of biology concerning biological activity at the molecular level. The field of molecular biology overlaps with biology and chemistry and in particular with genetics and biochemistry.
molecular switch
A molecule that can be reversibly changed between two or more stable states.
A molecule that "can undergo polymerization thereby contributing constitutional units to the essential structure of a macromolecule".
motor neuron
A neuron whose cell body is situated in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly control effector organs, mainly muscles and glands.
mucous membrane
A membrane that lines various cavities in the body and covers the surface of internal organs.
Having or consisting of more than one cell, as opposed to being unicellular.
The branch of biology concerned with the study of fungi, including their genetic and biochemical properties, their taxonomy and their use to humans as a source for tinder, medicine, food, and entheogens, as well as their dangers, such as poisoning or infection.
A basic rod-like unit of a muscle cell.
A superfamily of motor proteins best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes.

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natural selection
A process in nature in which organisms possessing certain genotypic characteristics that make them better adjusted to an environment tend to survive, reproduce, increase in number or frequency, and therefore, are able to transmit and perpetuate their essential genotypic qualities to succeeding generations.

Also called neuroscience.

The scientific study of the nervous system.
An electrically excitable cell that receives, processes, and transmits information through electrical and chemical signals.
An endogenous compound that enable neurotransmission.
The role and position an organism or taxon fills within its environment; how it meets its needs for food and shelter, how it survives, and how it reproduces. A species' niche includes all of its interactions with the biotic and abiotic factors of its environment.
nucleic acid
The biopolymers, or small biomolecules, essential to all known forms of life .
nucleic acid sequence
A succession of letters that indicate the order of nucleotides forming alleles within a DNA or RNA molecule.
The nitrogen-containing biological compounds that form nucleosides, which in turn are components of nucleotides, with all of these monomers constituting the basic building blocks of nucleic acids.
An irregularly shaped region within the cell of a prokaryote that contains all or most of the genetic material, called the genophore.
The largest structure within the nucleus of eukaryotic cells.
An organic compound which serves as the fundamental monomer used in the construction of nucleic acid polymers, such as DNA and RNA, both of which are essential biomolecules within all living organisms.

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A collection of tissues joined in a structural unit to serve a common function.
A contiguous living system.
The branch of zoology that concerns the study of birds. Etymologically, the word "ornithology" derives from the ancient Greek ὄρνις ornis ("bird") and λόγος logos ("rationale" or "explanation").
The spontaneous net movement of solvent molecules through a semipermeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides.

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The study of the history of life on Earth as reflected in the fossil record. Fossils are the remains or traces of organisms (plants, animals, fungi, bacteria and other single-celled living things) that lived in the geological past and are preserved in the crust of the Earth.
parallel evolution
The development of a similar trait in related, but distinct, species descending from the same ancestor, but from different clades.
The study of parasites, their hosts, and the relationship between them. As a biological discipline, the scope of parasitology is not determined by the organism or environment in question, but by their way of life.
The study or practice of pathology with greater emphasis on the biological than on the medical aspects.
A medical specialty that is concerned with the diagnosis of disease based on the laboratory analysis of bodily fluids such as blood and urine, as well as tissues, using the tools of chemistry, clinical microbiology, hematology and molecular pathology.
A numeric scale used to specify the acidity or basicity (alkalinity) of an aqueous solution. It is roughly the negative of the logarithm to base 10 of the concentration, measured in units of moles per liter, of hydrogen ions.
The science of drug action on biological systems. In its entirety, it embraces knowledge of the sources, chemical properties, biological effects and therapeutic uses of drugs.
The composite of an organism's observable features or traits, such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior.
A secreted or excreted chemical factor that triggers a social response in members of the same species.
The conducting tissue in plants responsible for the conduction of food particles.
The branch of biology dealing with the functions and activities of living organisms and their parts, including all physical and chemical processes.
The study of phytochemicals, which are chemicals derived from plants.
The science of diagnosing and managing plant diseases.
A substance or treatment of no intended therapeutic value.
The process in which cells lose water in a hypertonic solution.
The transfer of pollen from a male part of a plant to a female part of a plant, enabling later fertilisation and the production of seeds, most often by an animal or by wind.
A large macromolecule composed of many repeated subunits.

polymerase chain reaction (PCR)
A technique used in molecular biology to amplify a single copy or a few copies of a segment of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence.
Having or containing more than two complete sets of chromosomes.
population biology
The study of populations of organisms, especially the regulation of population size, life history traits such as clutch size, and extinction.
population ecology
A subfield of ecology that deals with the dynamics of species populations and how these populations interact with the environment. It is the study of how the population sizes of species change over time and space. Also called autoecology.
A biological interaction in which a predator kills and eats its prey.
A type of RNA polymerase involved in the replication of DNA.
A short strand of RNA or DNA that serves as a starting point for DNA synthesis.
Any genetic descendant or offspring.
An endogenous steroid and progestogen sex hormone which is part of the menstrual cycle, pregnancy, and embryogenesis of humans and other animal species.
An organism which does not have a true nucleus.
A polypeptide chain of amino acids. It is a body-building nutrient.
protein structure
A three-dimensional arrangement of atoms in an amino acid-chain molecule.
The application of the principles of biology to the study of physiological, genetic, and developmental mechanisms of behavior in humans and other animals. Also called behavioral neuroscience, biological psychology, and biopsychology.

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Giving birth to one of its kind, sexually or asexually.
reproductive biology

ribonucleic acid (RNA)
A nucleic acid polymer composed of a series of ribonucleotides which incorporate a set of four nucleobases: adenine (A), guanine (G), cytosine (C), and uracil (U). Closely related to DNA, RNA molecules serve in a wide variety of essential biological roles, including coding, decoding, regulating, and expressing genes, as well as functioning as signaling molecules.
A complex molecular machine, found within all living cells, that serves as the site of biological protein synthesis.
See ribonucleic acid.
RNA polymerase
A member of a family of enzymes that are essential to life: they are found in all organisms and many viruses.


A type of tissue in which cells have thick lignified secondary walls and often die when mature.
The embryo, enclosed in a protective outer covering, of certain types of plants.
selective breeding
See artificial selection.
sexual reproduction
A type of reproduction in which cells from two parents unite to form the first cell of a new organism.
The degree to which individuals in an animal population tend to associate in social groups and form cooperative societies.
A field of scientific study that is based on the hypothesis that social behavior has resulted from evolution and attempts to explain and examine social behavior within that context.
soil biology
The study of microbial and faunal activity and ecology in soil.
The basic unit of classification and a taxonomic rank, as well as a unit of biodiversity, but it has proven difficult to find a satisfactory definition.
The evolutionary process by which populations evolve to become distinct species.
stem cell
The biological cells that can differentiate into other types of cells and can divide to produce more of the same type of stem cells.
A biologically active organic compound with four rings arranged in a specific molecular configuration.
structural biology
The branch of molecular biology, biochemistry, and biophysics concerned with the molecular structure of biological macromolecules, especially proteins and nucleic acids, how they acquire the structures they have, and how alterations in their structures affect their function.
An evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms occurring from symbiosis.
Any close and long-term biological interaction between two different biological organisms, regardless of the nature or degree of the effect on either organism. Examples include mutualism, commensalism, and parasitism.
synthetic biology
An interdisciplinary branch of biology and engineering. The subject combines various disciplines from within these domains, such as biotechnology, evolutionary biology, molecular biology, systems biology, biophysics, computer engineering, and genetic engineering.
The scientific study of biodiversity. It is concerned with the discovering and naming of new species of organisms (nomenclature) and arranging these taxa into classification schemes (taxonomy). A large part of modern systematics concerns establishing the evolutionary relationships among various taxa (phylogenetics) using methods of comparative biology (e.g. physiology, behavior, biochemistry, morphology, genetics) and statistical analysis.
systems biology

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T cell
A type of lymphocyte that plays a central role in cell-mediated immunity.
A group of one or more populations of an organism or organisms seen by taxonomists to form a unit.
The primary male sex hormone and an anabolic steroid.
One of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T.
Transcription is the first step of gene expression, in which a particular segment of DNA is copied into RNA (mRNA) by the enzyme RNA polymerase. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language.
The process in which ribosomes in the cytoplasm or ER synthesize proteins after the process of transcription of DNA to RNA in the cell's nucleus.
trophic level
The position an organism occupies in a food chain.

Also called a neoplasm.

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Having or consisting of only one cell, as opposed to being multicellular.
One of the four nucleobases in the nucleic acid of RNA that are represented by the letters A, G, C and U.
An organic compound with chemical formula CO(NH2)2.
A liquid byproduct of metabolism in humans and in many animals.
A major female hormone-responsive secondary sex organ of the reproductive system in humans and most other mammals.


A membrane-bound organelle which is present in all plant and fungal cells and some protist, animal and bacterial cells.
valence electron
A valence electron is an electron that is associated with an atom, and that can participate in the formation of a chemical bond; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.
The widening of blood vessels.
vegetative reproduction
The type of reproduction in which sexual process is not involved, also known as asexual reproduction.
A small structure within a cell, or extracellular, consisting of fluid enclosed by a lipid bilayer.
The retention during the process of evolution of genetically determined structures or attributes that have lost some or all of their ancestral function in a given species.
The branch of biology that studies viruses
A submicroscopic, infectious, parasitic particle of genetic material contained in a protein coat and which replicates only inside the living cell of a host organism.

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white blood cell
See leukocyte.
whole genome sequencing
The process of determining the complete DNA sequence of an organism's genome at a single time.
wobble base pair
A pairing between two nucleotides in RNA molecules that does not follow Watson-Crick base pair rules.
The inner layer of the stems of woody plants, composed of xylem.


The yellow colored photosynthetic pigments.
The plant tissue responsible for the conduction of water from roots to aerial parts of the plant. It forms the woody part of the plant.


The nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo.


The branch of biology that studies the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems.
Are heterotrophic (sometimes detritivorous) plankton (cf. phytoplankton). Plankton are organisms drifting in oceans, seas, and bodies of fresh water. Individual zooplankton are usually microscopic, but some (such as jellyfish) are larger and visible to the naked eye.
A diploid reproductive stage in the life cycle of many fungi and protists.
A eukaryotic cell formed by a fertilization event between two gametes.

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See also


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